How could decision tree learning algorithms cope with imbalanced classes?
Decision Tree learners, on their own, are not a good way to deal with imbalanced data. The most commonly used algorithms, by default, make no attempt to address this problem.

If you look carefully at the three sources you post, you will find that they actually all agree on this point.

Two of the sources actually propose methods of addressing this shortcoming, by making adjustments to the decision tree learning algorithms. The proposed adjustments are essentially standard solutions to these problems, being applied to decision trees.

An example technique, discussed in the first paper you reference, is changing the weightings of the classes. An inefficient/approximate way to do this is to increase the number of examples from the minority class. For example, if you had an 80/20 split, you could add 3 new copies of each minority class example to move to an 80/80 = 50/50 split. Of course, if you add new data points, your algorithm may take longer to run. Instead, you can just modify the weightings of the classes in your optimization function. This approach is algorithm-specific, and will depend on your loss function, but achieves the same effect, just without needing to increase the number of points you use.